IDH1 and central nervous system cancer: In the Classical cluster, which consists uniformly of WHO CNS5 “glioblastomas, IDH-wildtype”, half of the cases (55 out of 108 tumors) were “molecular glioblastomas” (i.e., histologically lower-grade gliomas but with the molecular features of a glioblastoma), which were previously classified as grade II-III astrocytomas, oligoastrocytomas, and oligodendrogliomas.